Method of separating colour emulsion from acetate back colour transparencies



United States Patent 2,992,100 METHOD OF SEPARATING COLOUR EMUL- SION FROM ACETATE BACK COLOUR TRANSPARENCIES Keay Harold C. Grant, 4 Glen Muir Drive, Toronto,

Ontario, Canada, and James L. Bacon, Main St., Uni'onville, Ontario, Canada No Drawing. Filed Feb. 18, 1957, Ser. No. 640,611

2 Claims. (Cl. 96-2) This invention relates to the colour photography art, 7

and more particularly to an improved method whereby the colour emulsion may be removed intact from the cellulose acetate'baoking on which the emulsion is bonded on a colour transparency and remounted upon glass or any other transparent medium.

As is well known in the art, developed colour transparencies consist of a cellulose acetate backing to which there is bonded (on one side) the colour emulsion which forms the actual picture and (on the other side) an anti-halation coating such as gelatin or the like adapted to prevent the reflection of light from the obverse side of the acetate. The colour emulsion itself is of laminated construction consisting of successive layers of the 3 primary colours with filters and bonding agents therebetween, the whole colour emulsion being of the order of .002 or .003 inch thick.

It is also well known in the art that for many applications, and in particular for photo-engraving of colour slides, it is desirable to mount the colour emulsion upon glass after having removed it from its acetate backing. The shooting of a colour slide through glass by a photoengraving camera is by far the easiest, cheapest and most satisfactory method of making a colour engraving.

So far as is known, there is only one principal method in use today for the removal of the colour emulsion from the. acetate backing. This is a method used by the Eastman-Kodak Company. So far as is known, this method consists in plunging the print into a hot water bath containing chemicals such as an other solution which partially dissolves the acetate backing and loosens the bond between emulsion and backing. After a certain amount of soaking in this bath, the procedure is to peel the emulsion from the backing manually, whereupon the wet emulsion may be applied to any other surface.

There are several notable disadvantages to this process including:

(1) The fact that it is necessary to soak the whole print is in itself a serious disadvantage. The difiiculty of working with wet acetate and emulsion is well known in the photographic art. The emulsion when wet becomes extremely sticky and must be handled with the utmost care to prevent curling, tearing or other damage.

(2) The fact that it is necessary to soak the whole print makes it necessary to stretch the print prior to afiixinent to the backing since the wet emulsion has a tendency to shrink upon drying, and such shrinking would cause distortion of the original image.

(3) The requirement for manual peeling of the emulsion from the acetate is delicate and diflicult. Many prints are lost through tearing, and the process is, even when successful, time consuming and correspondingly expensive.

It is an object of this invention, therefore, to provide a method of removing colour film emulsion from the cellulose acetate backing of colour transparencies without the necessity of wetting the entire print, or passing it into or through liquid baths.

It is a further object of this invention to provide such a method that will be more reliable than has heretofore been possible.

It is another object of the invention to provide such ice a method as will simplify the former procedure and require no manual peeling of the acetate from the emulslon.

It is a still further obiect of the invention to provide such a method as will materially reduce the cost of stripping and remounting such emulsions.

These and other advantageous objects will become apparent through a consideration of the following detailed description.

The invention consists broadly in removing the cellulose acetate backing from a colour transparency by (1) Covering the emulsion surface with a layer of a clear, transparent waterproof, plastic coating, which is inert to sodium hypochlorite,

(2) Removing the anti-halationcoating by swabbing with sodium hypochlorite or an aqueous solution thereof,

3) Saturating the acetate with a solvent and removing the dissolved acetate'by scraping or swabbing, and

(4) Coating the acetate side of emulsion as in 1).

In greater detail, the method of the invention is as follows:

The transparency is preferably first coated, on the emulsion side, with a clear, waterproof coating which is inert to sodium hypochlorite. This preliminary coating is not absolutely necessary, but for reasons which will become apparent hereafter, it constitutes a preferred step in the practice of the invention.

' A coating which has been used with good results is marked under the trade name Protectocoafiand is manufactured by Sigma Products, Newton, New I ersey, U.S.A.

Any coating which meets the requirements of (a) transparency (b) water repellence and (c) inertness to sodium hypochlorite may be used with equally effective results. Thus, we have used, for example as a substitute for the Protectocoat a coat-ing of substantially equal parts of ether, acetate, and banana oil.

The thus coated emulsion may then be conveniently placed, emulsion side down, on a flat sheet such as glass, and the edges sealed to the glass by cellulose tape, masking tape or any other chemically inert water-proof seal.

The anti-halation backing may then be removed with sodium hypochlorite or an aqueous solution thereof.

It has been found that the anti-halation backing is readily soluble in sodium hypochlorite and the backing may easily be removed merely by application of the sodium hypochlorite followed by a light swabbing with cotton batting or any non-abrasive swab soaked in sodium hypochlorite. A sponge soaked in sodium hypochlorite may also be used both to apply the solution and to rub ed the dissolved backing.

After the anti-halation backing has been removed, the transparency, still sealed to the glass, with the acetate backing now exposed, is coated with a solvent. The solvent must be one capable of dissolving the cellulose acetate but inert to the film emulsion, and many such compounds are well known in the art. Among the more effective is acetone which will readily dissolve the acetate but leave the emulsion unharmed. A product marketed under the trade name Methyl Cellosolve Acetate (ethylene glycol monomethyl ether acetate) is also effective. It is understood that this compound is primarily a solution of ether. The choice of such compounds is well within the skill of the art, and when here and elsewhere in this specification and claims we use the term solvent, it is to be understood as meaning a solution capable of dissolving cellulose acetate but inert to the colour emul- $1011.

The solvent may be applied with a sponge, brush, or by merely flowing it over the now exposed acetate backmg.

After the backing has been softened by the action of the solvent, it will become tacky and gummy, and may readily be removed from the colour emulsion by scraping with a non-abrasive scraping edge (such as a rubber squeegee or a cardboard scraper) or rubbed off with solvent saturated swabs.

A clear transparent coating, similar to that initially used to coat the emulsion side, may now be applied to the emulsion thus exposed, and, the emulsion is isolated and ready for remounting. v

The use of the transparent coating initially protects the colour emulsion face against the action of sodium hypochlorite which might conceivably seep under the masking tape. Coating both sides of the emulsion renders the isolated emulsion waterrepellent and helps to overcome many of the disadvantages associated with the handling of wet emulsions.

Remounting of the .isolated emulsion is well within the scope of the competent workmen in the art, many bonding compositionsbeing well known for such purpose. A product manufactured and sold by the Eastman- Kodak Company known in the trade as stripping film cement will be found suitable for the purpose.

The emulsion may be mounted upon glass, or any other flat surface, but for engraving purposes, a glass backing will invariably be used.

The invention has been described in detail, and all the preferred steps and substances have been set forth. It is to be understood, however, that the invention is not limited to these precise details. Obvious variations still the scope of the invention will be apparent to those skilled in the art, and such embodiments of the invention as come within the scope and purview of the appended claims are to be considered as part of this invention.

What We claim is:

1. A process for removing a colour emulsion from a film transparency consisting of a cellulose acetate backing having a colour emulsion insoluble in an organic solvent selected from the group consisting of acetone and ethylene glycol monomethyl ether acetate bonded to one side and coated on the other side with a sodium hypochlorite soluble anti-halation coating which comprises (1) placing the emulsion side of the transparency against a flat surface and completely sealing the edges thereof to said flat surface;

(2) removing the anti-halation coating by selectively swabbing said coating with sodium hypochlorite; and

(3) removing the cellulose acetate backing by swabbing the exposed surface thereof with a solvent selected from the group consisting of acetone and ethylene glycol monomethyl ether acetate.

2. The process of claim 1 wherein the color emulsion is coated with a clear waterproof coating before the transparency is sealed to said flat surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,337 Stand Apr. 10, 1934 2,059,884 Mannes et a1 Nov. 3, 1936 2,173,480 Jung Sept. 19', 1939 2,251,365 Miller Aug. 5, 1941 2,293,816 Glafkides Aug. 25, 1942 2,357,590 Jatfe Sept. 5, 1944 2,393,027 Duerr et a1. Jan. 15, 1946 2,448,861 Colt Sept. 7, 1948 2,575,970 Nagel Nov. 20, 1951 FOREIGN PATENTS 19,810 Great Britain 1893 523,058 Great Britain July 4, 1940 OTHER REFERENCES Ranger et al.: Fiat Final Report 721, The Agfacolor Negative-Positive Method for Professional Motion Pictures, January 30, 1946 (copy in 

1. A PROCESS FOR REMOVING A COLOUR EMULSION FROM A FILM TRANSPARENCY CONSISTING OF A CELLULOSE ACETATE BACKING HAVING A COLOUR EMULSION INSOLUBLE IN AN ORGANIC SOLVENT SELECTED FROM THE GROUP CONSISTING OF ACETONE AND ETHYLENE GLYCOL MONOMETHYL ETHER ACETATE BONDED TO ONE SIDE AND COATED ON THE OTHER SIDE WITH A SODIUM HYPOCHLORITE SOLUBLE ANTI-HALATION COATING WHICH COMPRISES (1) PLACING THE EMULSION SIDE OF THE TRANSPARENCY AGAINST A FLAT SURFACE AND COMPLETELY SEALING THE EDGES THEREOF TO SAID FLAT SURFACE; (2) REMOVING THE ANTI-HALATION COATING BY SELECTIVELY SWABBING SAID COATING WITH SODIUM HYPOCHLORITE; AND (3) REMOVING THE CELLULOSE ACETATE BACKING BY SWABBING THE EXPOSED SURFACE THEREOF WITH A SOLVENT SELECTED FROM THE GROUP CONSISTING OF ACETONE AND ETHYLENE GLYCOL MONOMETHYL ETHER ACETATE. 